Re: [PATCH RFT 0/2/2] mtd: hyperbus: add Renesas RPC-IF driver

[Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>]

On Thu, 20 Feb 2020 08:46:23 +0100
Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> wrote:

> On Wed, 19 Feb 2020 23:13:36 +0300
> Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx> wrote:
> 
> > > One way would be to extend spi_mem_op to support above template along
> > > with a new field to distinguish SPI NOR vs HyperFlash protocol. HyperBus
> > > core can then register a spi_device and use spi-mem ops to talk to
> > > controller driver.    
> > 
> >    We have discussed this idea with Mark Brown, the SPI maintainer, and
> > he wasn't terribly impressed (I've invited him to #mtd -- his nick is
> > broonie and mine is headless, I'm also adding him to CC:).
> >   
> > > So, I suggest making Renesas RPC-IF backend a full fledged spi-mem
> > > driver (instead of driver/memory) and use extended spi_mem_op to support
> > > HyperFlash.    
> > 
> >    I don't think cramming support for the different flash busses into
> > the SPI drivers is a good idea...  
> 
> That's what I thought at first (SPI and Hyperflash seemed different
> enough to not merge them), then I had a look at Vignesh's HyperFlash
> presentation [1], and there's one aspect that made me reconsider this
> PoV. Slide 25 (xSPI compliant HyperFlash): having devices bouncing from
> one driver to another depending on the mode they operate in is likely to
> be painful to handle. Not to mention that Octo+DTR is similar to
> HyperBus from an HW PoV (at the PHY level, they both have CS, CLK,
> DQS/RWDS, DQ/IO[0:7] signals, only the protocol differs).

This doc [2] also shows the similarities between HyperBus and
Octal+DTR-SPI.

> 
> [1]https://elinux.org/images/3/38/HBMC-v1.pdf

[2]https://www.st.com/content/ccc/resource/technical/document/application_note/group0/91/dd/af/52/e1/d3/48/8e/DM00407776/files/DM00407776.pdf/jcr:content/translations/en.DM00407776.pdf


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